Backlighted liquid crystal display using light passage member for more nearly uniform illumination

ABSTRACT

A liquid crystal display panel having a backlight for providing high brightness, uniformity of illumination intensity, small thickness, high efficiency and which can be manufactured at a low cost. The display device includes a liquid crystal display panel, a light source for illuminating the liquid crystal panel, a light passage member which can be formed of either transparent or translucent material disposed between the liquid crystal panel and the light source. The light source inlet side of the light passage member is formed with a recess so that the thickness is reduced at the region opposed to the brightest region of the light source. A light reflecting member substantially surrounds the light source and the light passage member is formed with an opening facing the liquid crystal panel to expose a surface portion of the light passage member. The light source can either be incandescent light bulb or a cold-cathode discharge tube. In the latter case, a thermistor is coupled in series with the tube to stabilize its temperature and hence stabilize the illumination intensity against changes in ambient temperature.

This is a division of application Ser. No. 245,856, filed Mar. 20, 1981,now U.S. Pat. No. 4,487,481.

BACKGROUND OF THE INVENTION

The present invention relates to a liquid crystal display deviceincluding an illumination unit.

Recently, as the characteristics of liquid crystal display devices havebeen improved, the range of application of liquid crystal displaydevices has increased. When liquid crystal display devices are used intoys, clocks, clerical machines, terminal units, automobiles, etc., itis necessary to provide an illumination device which is operable forlong periods of time, which has a relatively large panel area, and whichis decorative and efficient.

A liquid crystal display device having a backlight unit with a smalllamp has been employed for wristwatches. The backlight for such awristwatch display is used to illuminate the face of the watch to makeit possible to read the time at night. Conventional types of backlightsfor liquid crystal display devices are not fully satisfactory inbrightness, illumination intensity uniformity and decorative effect.Accordingly, it would be desirable to provide a liquid crystal displaydevice with a backlight which satisfies the above-describedrequirements, is thin, highly efficient and can be manufactured at a lowcost.

SUMMARY OF THE INVENTION

A liquid crystal display device including a liquid crystal panel, alight source for illuminating the liquid crystal panel, a light passagemember made of one of transparent and translucent material with thelight passage member being disposed between the liquid crystal panel andthe light source, and a light reflecting member substantiallysurrounding the light source and the light passage member with the lightreflecting member having an opening facing the liquid crystal panel toexpose a surface portion of the light passage member is provided. Apluarlity of recesses can be formed on the exposed surface portion ofthe light passage member to scatter light passing therethrough or aplurality of beads of plastic or glass may be disposed on the exposedsurface portion or the light passage member to scatter light passingtherethrough. In one embodiment, the length of the light path betweenthe light source and the exposed surface portion is uniform throughoutthe light passage member.

A light scattering member may also be disposed between the liquidcrystal panel and the light passage member. The reflecting member can bea base member of a material such as stainless steel and silver coatedwith a material selected from the group of aluminum, nickel and silver.The light passage member can be made of a transparent plastic resin andthe reflecting member can be a metal plate, a metal film or a laminatedsheet of aluminum and plastic adhered to the surface portions of thelight passage member other than the opening provided therein.

The light source may be an elongated or linear light source and thelight passage member may have a space in a light inlet side thereof inwhich the linear light source is disposed. Alternatively, a linear lightsource may be disposed in a lower central portion of the display deviceoverlapping with the display panel in plan view and a light scatteringmember disposed between the display panel and the linear light source.In this case, the thickness of the light scattering member is preferablygradually reduced towards the end portions thereof in the direction ofthe length of the light source. In one embodiment, the light scatteringmember is made of milky colored polycarbonate resin or milky coloredacrylic resin. The thickness of the light scattering member can bereduced gradually towards the end portions thereof in a directionorthogonal to the length of the light source. The linear light source ina preferred embodiment is a cold-cathode discharge tube. In otherembodiments, the reflecting member may be a metal plate of the materialselected from Ag, Fe and stainless steel or may be a metal plate coatedwith one of Al, Ni and Ag.

A wavelength selection filter may be disposed between the liquid crystalpanel and the light source. Preferably, the filter is a sharp-cut filterwhich blocks ultraviolet rays. The cold-cathode discharge tube can bemounted so as to be biased towards a base plate disposed on one side ofthe light passage member. There is further preferably included adischarge stabilizing resistor disposed outside the base plate and thelight scattering and reflecting member and positioned between the baseplate and the discharge tube. The liquid crystal panel can be a coloredliquid crystal panel and may include a dichromatic filter. A temperaturedetector may be disposed near a wall of the cold-cathode discharge tubewith the temperature detector coupled to a circuit for controlling adischarge voltage of the tube. The temperature detector may include athermistor connected in series with the discharge tube.

The light source may be an incandescent light bulb with a wave lengthselection filter disposed between a liquid crystal layer of the liquidcrystal panel and the bulb. This filter preferably blocks red lightwhile passing blue light. The wavelength selection filter may be in theform of a cup covering the bulb.

Accordingly, it is an object of the invention to provide an improvedliquid crystal display device.

It is a further object of the invention to provide an improved liquidcrystal display device including a backlighting unit.

It is another object of the invention to provide a liquid crystaldisplay device with an improved backlight unit for providing uniformillumination intensity.

Still a further object of the invention to provide an improved backlightunit including a cold-cathode discharge tube for a thermistor in seriesfor stabilizing the temperature for providing uniform illumination tothe display.

Still another object of the invention is to provide an improvedbacklight unit for a liquid crystal display device utilizing anelongated cold-cathode discharge tube which includes a light scatteringmember adapted to provide uniform illumination to the display.

Still other objects and advantages of the invention will in part beobvious and will in part be apparent from the specification.

The invention accordingly comprises the features of construction,combination of elements, and arrangement of parts which will beexemplified in the construction hereinafter set forth, and the scope ofthe invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the invention, reference is had to thefollowing description taken in connection with the accompanyingdrawings, in which:

FIG. 1 is a cross-sectional view of a first embodiment of a liquidcrystal display device constructed in accordance with the presentinvention;

FIG. 2 is a cross-sectional view of a second embodiment of a liquidcrystal display device constructed in accordance with the presentinvention;

FIG. 3 is a cross-sectional view of a third embodiment of a liquidcrystal display device constructed in accordance with the presentinvention;

FIG. 4 is a cross-sectional view of a fourth embodiment or a liquidcrystal display device constructed in accordance with the presentinvention;

FIG. 5 is a cross-sectional view of a fifth embodiment of a liquidcrystal display device constructed in accordance with the presentinvention;

FIG. 6 is a cross-sectional view of a sixth embodiment of a liquidcrystal display device constructed in accordance with the presentinvention;

FIG. 7 is a cross-sectional view of a seventh embodiment of a liquidcrystal display device constructed in accordance with the presentinvention;

FIG. 8 is a cross-sectional view of an eighth embodiment of a liquidcrystal display device including an elongated light source in accordancewith the invention;

FIG. 9 is a plan view of a backlighted liquid crystal display deviceincluding an elongated light source as in FIG. 8 and modified inaccordance with the invention;

FIG. 10 is a front view of the device of FIG. 9;

FIG. 11 is a side view of the device of FIGS. 9 and 10;

FIG. 12 is a second modification of the device of FIG. 8;

FIG. 13 is a third modification of the device of FIG. 8;

FIG. 14 is a fourth modification of the device of FIG. 8;

FIG. 15 is a fifth modification of the device of FIG. 8;

FIG. 16 is a sixth modification of the device of FIG. 8;

FIG. 17 is a seventh modification of the device of FIG. 8;

FIG. 18 is a cross-sectional view of a further modification of thedevice of FIG. 1 including a wavelength selective absorbing filter;

FIG. 19 is a cross-sectional view of the device of FIG. 18 wherein thefilter is disposed between the panel and photoconductor;

FIG. 20 is a cross-sectional view of the device of FIG. 18 wherein thelower plate includes the filter;

FIG. 21 is a cross-sectional view of the device of FIG. 18 wherein thephotoconductor includes the filter;

FIG. 22 is a graph of the spectral characteristics of radiant flux ofnatural day light and a fluorescent light;

FIG. 23 is a graph showing the spectral characteristic of a liquidcrystal material;

FIG. 24 is a graph showing the spectral characteristic of a blue filter;

FIG. 25 is a circuit diagram for a circuit for operating a liquidcrystal display device of the invention including temperaturecompensating means;

FIG. 26 is another circuit diagram for a circuit for operating a liquidcrystal display device of the invention including temperaturecompensating means;

FIG. 27 is a graph of a tube current-temperature characteristic, anillumination intensity-temperature characteristic, and a dischargestarting voltage characteristic of a cold-cathode discharge tube;

FIG. 28 is a graph showing abient temperature-illumination intensitycharacteristic curves with tube current as a parameter of a cold-cathodedischarge tube;

FIG. 29 is a circuit diagram of a temperature-compensated circuit foroperating a cold-cathode discharge tube in a display device of theinvention;

FIG. 30 is a second circuit diagram of a temperature-compensated circuitfor operating a cold-cathode discharge tube in a display device of theinvention;

FIG. 31 is a third circuit diagram of a temperature-compensated circuitfor operating a cold-cathode discharge tube in a display device of theinvention;

FIG. 32 is a sectional front view of a further embodiment of a liquidcrystal display device of the invention;

FIG. 33 is a sectional side view of the device of FIG. 32;

FIG. 34 is a sectional front view of a still further embodiment of aliquid crystal display device of the invention;

FIG. 35 is a side view of the device of FIG. 34;

FIG. 36 is a sectional front view of still another embodiment of aliquid crystal display device of the invention;

FIG. 37 is a sectional side view of the device of FIG. 36;

FIG. 38 is a sectional view of an example of an opal light scatteringelement used in several embodiments of a liquid crystal display deviceof the invention;

FIG. 39 is another sectional side view of the element of FIG. 38; and

FIG. 40 is a front view of an example of a displayed pattern produced bya liquid crystal display device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment of a liquid crystal display device including anilluminating backlight constructed and arranged in accordance with theinvention is shown in FIG. 1. The device includes a liquid crystal panel1 which is made up of an upper electrode substrate 2, a lower electrodesubstrate 3, a liquid crystal 7, a spacer 6, an upper polarizing element4 and a lower polarizing element 5. Disposed behind panel 1 is a lightemitting element 8 which is inserted into an opening 9a formed in aphotoconductor 9. Photoconductor 9 is covered by a light scattering andreflecting element 10, except for a window 10a exposing a part ofphoto-conductor 9 through which light is applied to liquid crystal panel1 and aperture 10b through which electrical connecting components, suchas lead wires and the base of a socket for supplying current to thelight emitting element 8 pass.

Photoconductor 9 may be made of any transparent material, but ispreferably glass or an acryl material. Both glass and acryl absorb verylittle light energy as the light passes through and are free from doublerefraction. A glass plate has excellent transparency. On the other hand,an acrylic plate is advantageous in that it can be readily machined, itcan be shaped as desired by molding, and it can easily be manufacturedon a large scale. Additionally, an acrylic plate has the greatesttransparency among plastic plates.

Light emitting element 8 may be an incandescent light bulb, acold-cathode discharge tube or a small lamp using a tungsten filamentall of which are commercially available. In this connection, a varietyof small lamps, high power small lamps and low power small lamps arecurrently available from a number or manufacturers at relatively lowcost. When light emitting element 8 is a small lamp, it must be thin andis preferably of low price. If a cold-cathode discharge tube is used aslight emitting element 8, various benefits over an incandescent lamp areobtained. Specifically, a cold-cathode discharge tube emits white light,has a long service life, typically several ten thousands of hours, andhas a low power consumption.

Light scattering and reflecting element 10 can be an aluminum plate,aluminum foil, an aluminum and plastic lamination sheet, a metal platecoated with Al or Ni, or an aluminum reflecting plate with glass beads.Light scattering and reflecting element 10 is bonded to photoconductor 9or mechanically mounted thereon by mechanical pressure. Alternatively,light scattering and reflecting element 10 can be formed by theformation of a layer of aluminum or nickel on photoconductor 9 byvacuum-evaporating, sputtering, or by coating photoconductor 9 with amixture of aluminum or nickel in an adhesive or paint. It is necessarythat light scattering and reflecting element 10 be so designed thatlight emitted from light emitting element 8 is completely enclosedwithin photoconductor 9. To prevent light from leaking to the outside,it is necessary to cover light scattering element 10 with a white paintlayer, aluminum plate or aluminum foil, so that light scattering andreflecting element 10 can completely enclose the light in photoconductor9.

The emitting portion of light emitting element 8 is inserted into anopening 9a formed in photoconductor 9 with photoconductor 9 beingcovered by light scattering and reflecting element 10, except for window10a through which light is applied to the liquid crystal panel 1. Thus,the light from light emitting element 8 is scattered and is enclosed inphotoconductor 9 by light scattering and reflecting element 10 so as toilluminate liquid crystal panel 1 evenly through window 10a of lightscattering and reflecting element 10.

When photoconductor 9 and light scattering and reflecting element 10 areconstructed as described above, little light energy is absorbed byphotoconductor 9 and the reflection efficiency of light scattering andreflecting element 10 is high. Accordingly, almost all the light from anincandesent lamp utilized as light emitting element 8 illuminates liquidcrystal panel 1. That is, a liquid crystal display device having abacklight with a high efficiency is provided by the invention.Furthermore, the materials of photoconductor 9 and light scattering andreflecting element 10 are readily available at low cost and thesematerials can be machined readily. With a light emitting element 8 asdescribed above, the light emitting source is small, thin and of lowcost but yet it has a long service life.

Another embodiment of a liquid crystal display device according to theinvention can be obtained by modifying the device shown in FIG. 1 asfollows. As shown in FIG. 2, the surface 12b of a photoconductor 12disposed below a liquid crystal panel 11 is made uneven, such as bycutting V-shaped grooves 15 in the surface thereof. A light emittingelement 14 is inserted into an opening 12a in photoconductor 12 which iscovered by a light scattering and reflecting element 13. Uneven surface12b specifically the V-shaped grooves 15, can be formed by a mechanicaltechnique using abrasives or by a molding machine. The quantity of lightilluminating liquid crystal panel 11 is increased by the formation ofuneven surface 12b or V-shaped grooves 15 on photoconductor 12 with theresult that the efficiency of illumination is improved. The secondembodiment effectively provide a backlight which is soft in addition tothe improved efficiency of illumination. Accordingly, the liquid crystaldisplay device of this embodiment of the invention has an excellentbacklighting effect.

FIG. 3 shows a third embodiment of a liquid crystal display deviceaccording to the invention in which, instead of the above-describeduneven surface 12b or V-shaped grooves 15, plastic or glass beads 19 arearranged on surface 17b of a photoconductor 17 which is disposed behindand adjacent to a liquid crystal panel 16. A light emitting element 20is inserted into a hole 17a cut in the photoconductor 17. Photoconductor17 is covered by a light scattering and reflecting element 18, exceptfor an aperture 18b at the power supplying section of a light emittingelement 20 and a window 18a through which light is applied to liquidcrystal panel 16. Plastic or glass beads 19 are preferably about 5 to100 μm in diameter and are commercially available.

In this third embodiment shown in FIG. 3, light from light emittingelement 20 enclosed in photoconductor 17 illuminates liquid crystalpanel 16 through window 18a. In this operation, the light is irregularlyreflected by plastic or glass beads 19 as a result of which the userobserves a soft light. Thus, the third embodiment has the effect thatthe backlight provides excellent eye-appeal in addition to theadvantageous effects of the first embodiment shown in FIG. 1.Furthermore, the quantity of light illuminating liquid crystal panel 16is increased when compared with that in the case where plastic or glassbeads 19 are not used. This is another advantage of the thirdembodiment.

Plastic or glass beads 19 can be disposed on photoconductor 17 using anyof a number of available known techniques. Beads 19 can be secured tophotoconductor 17 by an adhesive agent or by thermal fusion.Additionally, beads 19 may be embedded in photoconductor 17 while heatedto a molten state. Alternatively, beads 19 may be adhered tophotoconductor 17 when the latter is molded. As shown in FIG. 3 beads 19are arranged uniformly. However, the same effect can be obtained byarranging beads 19 randomly or by the formation of two layers of beads19.

In a fourth embodiment of the liquid crystal display device of theinvention shown in FIG. 4, an opal light scattering plate 22 is disposedbetween a liquid crystal panel 21 and a photoconductor 23. A lightemitting element 25 is disposed in an opening 23a formed inphotoconductor 23. Photoconductor 23 is covered by a light scatteringand reflecting element 24, except for an opening 24b through which wirespass to light emitting element 25 and a window 24a through which lightis applied to liquid crystal panel 21.

Opal light scattering plate 22 may be an opal plastic plate such as anopal acrylic plate, an opal tellurinic plate, an opal film or an opalglass plate all of which are readily available. The same effect isobtained by including opal light scattering plate 22 as when an unevensurface or V-shaped grooves 12b are formed on the photoconductor orplastic or glass beads 19 are arranged on the photoconductor asdescribed above. If opal plate 22 is somewhat thick, the quantity oflight illuminating liquid crystal panel 21 will be reduced compared tothe construction of FIG. 1. However, it should be noted that employmentof opal light scattering plate 22 provides the following effects andadvantages. First, the quantity of light can be readily controlledcompared with the case where an uneven surface or V-shaped grooves 12bare formed or plastic or glass beads 19 are employed. Second, the lightscattering degree is determined by the thickness of opal plate 22 and,accordingly, as long as the plate thickness is uniform, the lightscattering degree is uniform throughout the area of the plate. Theliquid crystal display device shown in FIG. 4 can be manufacturedreadily by inserting opal light scattering plate 22 between liquidcrystal panel 21 and photoconductor 23.

FIG. 5 shows a fifth embodiment of a liquid crystal display deviceaccording to the invention. In this embodiment, an opal light scatteringplate 31 is inserted between a liquid crystal panel 26 and aphotoconductor 27. A light emitting element 29 is inserted into anopening 27a formed in the photoconductor 27. Photoconductor 27 iscovered by a light scattering and reflecting element 28, except for awindow 28a on the upper surface 27b of photoconductor 27 which confrontsliquid crystal panel 26 through opal light scattering plate 31. Uppersurface 27b of photoconductor 27 is made uneven or formed with V-shapedgrooves 30. Alternatively plastic or glass beads may be disposed onupper surface 27b. The quantity of light illuminating liquid crystalpanel 26 is increased compared with that in the case wherein uppersurface 27b remains even or when V-shaped grooves are not formedtherein. If grooves 30 are not uniform, the light is irregularly appliedto liquid crystal panel 26. However, this irregularity is substantiallycorrected by opal light scattering plate 31; and accordingly, liquidcrystal plate 26 is illuminated uniformly.

A sixth embodiment of a liquid crystal display device according to theinvention is shown in FIG. 6. In the sixth embodiment, a light emittingelement 35 is inserted into an opening 33a formed in a photoconductor 33which is covered by a light scattering and reflecting element 34 with awindow 34a formed on the upper surface 33b of photoconductor 33 forilluminating a liquid crystal panel 32. If photoconductor 33 has auniform thickness, the intensity of light is decreased in inverseproportion to the square of the distance from light source 35 to panel32. In other words, if photoconductor 33 is uniform in thickness, theintensity of the backlight is higher at positions closer to light source35 and is lower at positions further from light source 35. Accordingly,parts closer to light source 35 are viewed with a higher contrast andparts further from light source 35 with a lower contrast. In view ofthis fact, in the sixth embodiment, the thickness of photoconductor 33is decreased as the distance from an incandescent lamp as light source35 increases.

With respect to two light beams 36 and 37 which are emitted by lightsource 35, light beam 36 is scattered by a region 38 of light scatteringand reflecting element 34 closer to light source 35 as a result of whichlight beam 36 thus scattered is converted into a backlight beam 40illuminating a part of liquid crystal panel 32 closer to light source35. Light beam 36 is scattered by region 39 of light scattering andreflecting element 34 which is farther from light source 35 as a resultof which light beam 37 thus scattered is converted into a backlight beam41 illuminating a part of liquid crystal panel 32 farther from lightsource 35. The ratio of the intensity of light scattered by region 38 oflight scattering and reflecting element 34 to the intensity of lightscattered by region 39 of element 34 corresponds to the ratio of thereciprocal of the square of the distance between light source 35 andregion 38 to the reciprocal of the square of the distance between lightsource 35 and region 39. Accordingly, the light scattering degree ofregion 38 is greater than that of region 39 by the value of this ratio.

On the other hand, the ratio of the illumination intensity of backlightbeam 40 to the illumination intensity of backlight beam 41 correspondsto the ratio of the product of the light scattering degree at lightscattering and reflecting element region 38 closer to light source 35and the reciprocal of the square of the thickness of photoconductor 33at light scattering and reflecting element region 38 to the product ofthe light scattering degree at light scattering and reflecting elementregion 38 farther from light source 35 and the reciprocal of the squareof the thickness of photoconductor 33 at light scattering and reflectingelement region 39. If the thickness of region 38 is equal to that ofregion 39, the illumination intensity of backlight beam 40 is higherthan that of backlight beam 41. Therefore, in the sixth embodiment, atlight scattering and reflecting element region 39 which is farther fromlight source 35, corresponding to a greater distance from light source35 than the point of light scattering and reflecting element 34 wherelight 36 emitted by light source 35 is reflected, photoconductor 33 ismade thinner at light scattering and reflecting element region 39farther from light source 35 so that the intensity of backlight beam 41farther from light source 35 approaches that of backlight beam 40 closerto light source 35.

In order to accomplish this, the bottom 33' of photoconductor 33 slopesin a straight line from one side of the photoconductor 33 towards theopposite side. As a result, the intensity of backlight beam 41 fartherfrom light source 35 is substantially equal to that of backlight beam 40closer to light source 35. Accordingly, when liquid crystal panel 32 isilluminated by backlight beams 40 and 41, the brightness and contrastproduced are substantially uniform throughout the area of the panel.This construction is suitable for the backlighting of a large liquidcrystal panel as well as the backlighting of a small liquid crystalpanel.

A seventh embodiment of a liquid crystal display device according to theinvention is shown in FIG. 7. In this embodiment, a light emittingelement 45 is inserted into an aperture 43a formed in a photoconductor43 which is covered by a light scattering and reflecting element 44 witha window 44a formed in the upper surface of the photoconductor 43through which a liquid crystal panel 42 is illuminated. In thisembodiment also, the thickness of photoconductor 43 is decreased as thedistance from light source 45 increases. However, it should be notedthat the bottom 44' of light scattering and reflecting element 44, andaccordingly the bottom 43' of photoconductor 43 is curved in such amanner that the thickness of photoconductor 43 is gradually reduced fromthe side of light emitting element 45 towards the opposite side. Theeffects of the seventh embodiment are similar to those of the sixthembodiment for providing substantially uniform brightness and contact ofbacklighting.

FIG. 8 illustrates an eighth embodiment of a liquid crystal displaydevice according to the invention. In this embodiment, a linear,elongated or cylindrical light source 46 is employed. A cylindricalincandescent lamp or a cylindrical cold-cathode discharge tube may beused for linear light source 46. In FIG. 8, only a photoconductor 47 andlinear light source 46 are shown. A liquid crystal panel is disposed ata position indicated by a dashed line 48.

Linear light source 46 is disposed to apply light to one side ofphotoconductor 47. Linear light source 46 and photoconductor 47 arecovered by a light scattering and reflecting element except for abacklight application window region 48 for the liquid crystal panel anda minimum number of holes through which, for instance, lead wires forsupplying current to linear light source 46 pass. In FIG. 8, the liquidcrystal panel and the light scattering and reflecting element are notshown.

A specific feature of the eighth embodiment is that photoconductor 47has a V-shaped recess 52 through which light is applied thereto. IfV-shaped recess 52 were not provided, the scattering degree of the lightemitted by light source 46 would be highest at the central portion 49 ofbacklight application window region 48 provided for the liquid crystalpanel and would be lower at a right end portion 50 and a left endportion 51. That is, the backlight intensity at central portion 49 wouldbe clearly different from that at right and left end portions 50 and 51.However, the provision of V-shaped recess 52 makes the light scatteringdegree at central portion 49 substantially equal to that at right andleft end portions 50 and 51. This is particularly well-suited forbacklighting of a large panel, such as a display in a clock terminalunit and as a display in an automobile. This construction also makes itpossible to use effectively a cylindrical incandescent lamp or acold-cathode discharge tube as linear light source 46. Furthermore,employment of V-shaped recess 52 makes the backlighting intensityuniform over a larger area of photoconductor 47. As a result of this, itis possible to make the area of backlight application window region 48large compared with the area of photoconductor 47. Thus, a liquidcrystal display unit with a backlight of small size and high efficiencyis provided according to this embodiment of the invention.

Use of a point light source, such as a small incandescent lamp as thelight source is advantageous in that only a small space is required forreceiving the light source which contributes to a reduction of theoverall size of the liquid crystal display device. However, use of apoint light source still suffers from problems in that the liquidcrystal panel is not uniformly illuminated by light from the point lightsource and the illuminating intensity varies at different portions ofthe liquid crystal panel. This difficulty becomes more significant asthe display area of the liquid crystal panel increases. The difficultymay be eliminated by using a plurality of point light sources. Use of alinear light source or a cylindrical light source is advantageous inthat the number of components is reduced, the backlight structure issimplified and the reliability is also increased. The troublesome andtime-consuming operation of replacing individual point light sources inthe case of failure is also eliminated. Furthermore, light emanatingfrom a linear or cylindrical light source is more uniform than that froma point light source, and therefore the former is preferable as thebacklight source for a large panel. However, it should be noted that thelinear light source does have some drawbacks in that the illuminationintensity in the central portion of the liquid crystal panel tends to behigher than that in peripheral portions. In addition, the length of theportion of the tube which emits actual light, that is, the effectivelight emission tube length, is shorter than the physical length of thetube. Therefore, when illuminating a liquid crystal panel longer thanthe effective light emission tube length, the illumination intensity ofthe central portion is often different from that of peripheral portions.Even if the display panel is of equal length to the effective lightemission tube length, the backlight section is large compared with thesize of the panel.

These shortcomings of the linear light source are overcome in accordancewith the eighth embodiment, as described above with reference to FIG. 8.Linear or cylindrical light source 46 is disposed beside photoconductor47 and V-shaped recess 52 is formed in the side of photoconductor 47which confronts light source 46. Accordingly, compared with the casewhere V-shaped recess 52 is not formed, backlight from linear orcylindrical light source 46 diffuses uniformly throughout a larger partof photoconductor 47 covering substantially the entirety ofphotoconductor 47. In addition, the length of linear or cylindricallight source 46 may be made equal to or less than the width of displayregion 48 of the liquid crystal panel. Thus, in accordance with theembodiment, a liquid crystal display device with a backlight of smallsize and high efficiency is provided.

FIGS. 9, 10 and 11 are a plan view, a front view and a side view,respectively, showing a modification of a backlighted liquid crystaldisplay device in which a V-shaped recess 53a is formed in aphotoconductor 53. In these figures, only photoconductor 53 and a linearlight source 54 are shown. In this embodiment linear light source 54 isinserted into an opening 53b formed in photoconductor 53. Accordingly,the light from linear light source 54 is somewhat more effectivelyenclosed in photoconductor 53 than that in the embodiment shown in FIG.8 thereby further improving the backlighting efficiency.

FIG. 12 shows a second modification of the backlighted liquid crystaldisplay device of FIG. 8 in which a linear or cylindrical light source56 is used. A V-shaped recess 57 formed in a photoconductor 55 has adifferent configuration from that shown in FIG. 8. However, the effectsobtained are substantially the same as that obtained by the device ofFIG. 8.

FIG. 13 shows a third modification of the backlighted liquid crystaldisplay device shown in FIG. 8. This device includes a linear lightsource 59 and a photoconductor 58 as shown in FIG. 13. The effects ofthis modification are the same as that of the embodiment shown in FIG.8.

FIG. 14 shows a fourth modification of the backlighted liquid crystaldisplay device shown in FIG. 8. Here, a polygonal light receiving recess62 is formed in a photoconductor 60. In FIG. 14, reference numeral 61designates a linear light source. The effects are similar to those ofthe device shown in FIG. 8.

FIG. 15 shows a fifth modification of the device shown in FIG. 8. Inthis embodiment, a light receiving recess 65 is formed by rounding thesharp angle of the V-shaped recess in FIG. 8, that is, light receivingrecess 65 has a configuration which is between a "V" and a "U" in shape.In FIG. 15, reference numeral 64 designates a linear light source andreference numeral 63 designates a photoconductor. In the device thusconstruced, the light is diffused somewhat more uniformly than in thedevice of FIG. 8.

FIG. 16 shows a sixth modification of the device shown in FIG. 8. Inthis embodiment, an elliptical light receiving recess 68 is formed in aphotoconductor 67. In FIG. 16, reference 66 designates a linear lightsource. The effect of the device in FIG. 16 is similar to that of thedevice in FIG. 8.

FIG. 17 shows a seventh modification of the device in FIG. 8 wherein acylindrical cold-cathode discharge tube is employed as a linear lightsource 70 mounted on one side of a substrate 71. A light scattering andreflecting element 72 is disposed on the side of substrate 71. Thesurface of a photoconductor 69 except a portion thereof confronting thesubstrate 71 is covered by light scattering and reflecting element 72with a liquid crystal backlighting window being formed therein.

In order for cold-cathode discharge tube 70 to emit light stably, it isnecessary to provide a discharge stabilizing resistor 74 which isdisposed on the opposed side of substrate 71 away from tube 70 and isconnected to tube 70 by lead wires 73. In this case, as dischargestabilizing resistor 74 is positioned near cold-cathode discharge tube70, a backlighted liquid crystal display device is provided which has asmall size with the discharge carried out stably. Since light scatteringand reflecting element 72 is provided between cold-cathode dischargetube 70 and substrate 71, the light is effectively utilized even ifsubstrate 71 is included. Thus, backlighting is provided with highefficiency.

FIG. 18 shows yet another embodiment of a liquid crystal display deviceaccording to the invention in which a wavelength selective absorbingfilter 79 is disposed between a light emitting element 75 and a liquidcrystal panel 78. In FIG. 18, reference numeral 76 designates aphotoconductor. The photoconductor 76 and the light emitting element 75are covered by a light scattering and reflecting element 77. If thelight shone on the liquid crystal by light emitting element 75 includesa component such as ultraviolet rays which may harm the liquid crystaland filter 79 can eliminate the harmful component.

It may also be desirable to provide a decorative effect by illuminatingliquid crystal display panel 78 with backlight of various colors. Thisrequirement can be satisfied by the employment of filter 79. Lightemitting element 75 has a coherent spectral characteristic irrespectiveof its type. However, the light emitted by the light emitting elementcan be converted into a backlight of desired color by the use ofwavelength selective absorbing filter 79. In this case, it goes withoutsaying that a double-color filter having two portions of differentfiltering characteristics may be used.

FIG. 23 shows an example of the spectral characteristic of a liquidcrystal. A variety of liquid crystals are available, althoughconventionally used liquid crystals have a color ranging roughly fromyellow to red. Even a white liquid crystal can have colors in thisrange.

FIG. 22 shows the spectral characteristics of the spectral radiant fluxof natural daylight by a solid line 94 and fluorescent light by a dashline 95. In the spectral characteristic of the fluorescent light thespectral radiant flux tends to decrease in the visible wavelength bandor the long wavelength band compared with natural daylight 94.Therefore, if a cold-cathode discharge tube is employed as backlightemitting element 75 for the liquid crystal panel 78, the reddish colorof the liquid crystal in liquid crystal panel 78 matches the spectralcharacteristics of the cold-cathode discharge tube in which the amountof red is reduced compared with that of natural daylight. Accordingly,when the backlight is turned on, the coloration of liquid crystal panel78 becomes rich which improves the decorative effect. Thus, thecold-cathode discharge tube can provide an appealing backlight for acolored liquid crystal panel such as a "guest/host" type liquid crystalpanel or a TN type liquid crystal panel with a color filter. In thiscase, the backlight may be somewhat corrected by filter 79 so that itscolor approaches natural daylight. Filter 79 need be used only when itis necessary to eliminate ultraviolet rays from the light emitted bycold-cathode discharge tube 75, or when it is desired to obtaindifferent backlight colors.

The liquid crystal material can be completely protected from harmfulultraviolet rays by using a sharp cut filter which eliminates lightwaves shorter than about 300 to 400 μm in wavelength, such as anultraviolet ray filter. In the case where an incandescent lamp isemployed as the light emitting element, the red of the liquid crystalappears more prominent and accordingly the color of the liquid crystalpanel is not quite so appealing as the color temperature of theincandescent lamp is about 2000° K. and the radiant light is somewhatreddish. Accordingly, the use of blue filters is preferable in order toimprove the appearance of liquid crystal panel 78 under illuminationwhich is close to that of natural daylight 94. FIG. 24 illustrates thespectral characteristic of a blue filter.

A filter having such a spectral characteristic cuts reddish light and iseffectively applicable where light emitting element 75 is anincandescent lamp. As the filter converts the spectral characteristic oflight emitted from the liquid crystal panel into one closer to thespectral characteristic of natural daylight, the display of liquidcrystal panel 78 is very appealing and provides an excellent decorativeeffect. In such a liquid crystal display device, filter 79 is disposedbetween liquid crystal panel 78 and light emitting element 75.Accordingly, the display device can be manufactured readily at a lowmanufacturing cost using an incandescent lamp which is readily availableat a low price.

The filter may also be a color temperature conversion filter. The filtermay be in the form of a cap, a plastic sheet, a plastic plate or asilicon rubber, polycarbonate or acryl paint which has a filteringeffect. The cap is placed about the light emitting element. The paintcan be applied directly to the light emitting element by spraying,brush, vacuum-evaporating, or by spinning. A wavelength selectiveabsorbing filter in the form of a cap is advantageous, as it can bedetachably placed over the light emitting element and it is low in cost.

In the case where liquid crystal panel 78 is a colored liquid crystalpanel such as a "guest/host" type liquid crystal panel or a TN typeliquid crystal panel with a double-colored filter, wavelength selectiveabsorbing filter 79 may be inserted between the liquid crystal panel 78and light emitting element 75 so that light having a spectralcharacteristic altered to be substantially the same as daylight in thevisible wavelength range is applied to liquid crystal panel 78. In thiscase, the "guest"0 color or the colors of the double-color filter arenot affected; and accordingly, the same appealing colors as thoseobserved under daylight appear. This effect is significant in the casewhere the spectral characteristic of an incandescent lamp employed aslight emitting element 75 is made equal to or similar to the spectralcharacteristic of daylight or, for instance, in the case where a colortemperature conversion filter or a blue filter is employed as optionalwavelength selective absorbing filter 79.

FIG. 19 shows still another embodiment of a liquid crystal displaydevice according to the invention in which a wavelength selectiveabsorbing filter 81 is inserted between a liquid crystal panel 80 and aphotoconductor 82. In FIG. 19, reference numeral 83 designates a lightemitting element, and 84 a light scattering and reflecting element. Theeffects of this embodiment are similar to those of the display deviceshown in FIG. 18.

In another embodiment of a liquid crystal display device as shown inFIG. 20, a liquid crystal panel 85 includes a lower glass plate 86 whichitself is employed as a filter. The device of FIG. 20, includes a lightemitting element 87, a photoconductor 88 and a light scattering andreflecting element 89, arranged as described above. This liquid crystaldisplay device provides the same effects as those of the display deviceof FIG. 18. The liquid crystal display device of FIG. 20 is advantageousin that, as lower glass plate (or substrate) 86 of liquid crystal panel85 is made of a material having a filtering effect, the number ofmanufacturing steps and the number of components necessary are reduced.

FIG. 21 shows another embodiment in which a photoconductor 91 has afiltering effect. The device in FIG. 21 includes a light emittingelement 92, a light scattering and reflecting element 93 and a liquidcrystal panel 90. The effects of this embodiment are the same as thoseof the embodiment shown in FIG. 18.

In the above-described various embodiments of a liquid crystal displaydevice according to the invention, the light emitting element is shownas being provided only at one position. However, a brighter and moreappealing liquid crystal display device can be obtained by providinglight emitting elements at two positions or at a number of positions.Additionally, in the above-described embodiments, the opening providedto receive the light emitting element is shown as being formed in theside of the photoconductor. However, the same effect can be obtained byforming the aperture in the upper surface or in the lower surface of thephotoconductor.

Circuits for use in operating the liquid crystal display device inaccordance with the invention as described above will now be discussed.

In FIG. 25, a cold-cathode discharge tube 121 is the light emittingelement and a pair of auxiliary resistors (RA₁) 122 for stabilizing thedischarge operation of cold-cathode discharge tube 121 are coupled to aresistor (RS₁) 123 for limiting the tube current I_(L). In FIG. 26 acold-cathode discharge tube 131 is coupled to a triggering coating layer132 for providing a stable discharge operation and is coupled to a tubecurrent limiting resistor (RS₂) 133.

In the circuits of FIGS. 25 and 26, a voltage of several hundred voltsis applied to the cold-cathode discharge tube and a current limitingresistor (RS₁ or RS₂) is connected in series with the cold-cathodedischarge tube. In a bipolar type arrangement as shown, in general, thedischarge starting voltage is several hundred volts. After the dischargehas been started, the tube voltage is constant at about 160 V. In thecase where the tube is used for illumination, the tube current I_(L) is,in general from about 5 to 15 mA. If the tube current is increased to 20to 25 mA or more, the tube will be damaged in a relatively short periodof time. The power consumption of the tube itself is, in general, afraction of one watt. The tube wall temperature is higher by 15° to 20°C. than the ambient temperature.

FIG. 27 is a graphical representation indicating the temperaturecharacteristic of a cold-cathode discharge tube, namely, a tube currenttemperature characteristic 141, an illumination intensity temperaturecharacteristic 142, and a discharge starting voltage temperaturecharacteristic 143. In FIG. 27, relative values are plotted on thevertical axis. It is apparent from FIG. 27 that the tube current and theillumination have peak values when the ambient temperature is about 50°C. while the discharge starting voltage has a minimum value when theambient temperature is about 50° C.

FIG. 28 shows ambient temperature-illumination intensity characteristiccurves with tube currents as parameters, namely, a temperaturecharacteristic curve 151 for a tube current of 10 mA, a temperaturecharacteristic curve 152 for a tube current of 8 mA a temperaturecharacteristic curve 153 for a tube current of 7 mA a temperaturecharacteristic curve 154 for a tube current of 6 mA and a temperaturecharacteristic curve 155 for a tube current of 5 mA. It is clear fromFIG. 28 that the illumination intensity has a maximum value when theambient temperature is about 50° C. irrespective of the tube current. Ifthe ambient temperature is constant, as the tube current increases, theillumination intensity increases.

FIGS. 29 and 30 are circuit diagrams showing first and secondembodiments of a circuit of the invention in which a first positivecharacteristic thermistor (RS₁ ') 161 and a second positivecharacteristic thermistor (RS₂ ') 171 are connected in series withcold-cathode discharge tubes 162 and 172, respectively. In FIGS. 29 and30, reference numerals 164 and 174 designate stabilizing resistors (RS₁and RS₂), 165 auxiliary resistors (RA₁) and 175 a triggering coatinglayer. As in the arrangement shown in FIG. 25 including tube currentlimiting resistor 123, thermistors 161 and 171 are disposed on the tubewall or near the tube. In FIG. 29, auxiliary resistors provided formaintaining a stable discharge operation are located in a tube region163 designated by a dashed line. In FIG. 30, triggering coating layer175 is provided in a tube region 173 designated by a dashed line. Thecircuit of FIG. 29 is the same as that of FIG. 30 except for thestructure of tube regions 163 and 173. FIGS. 29 and 30 can be redrawn asshown in FIG. 31 in which a tube region 183 designated by a dashed linecorresponds to tube regions 163 and 173, respectively, of FIGS. 29 and30. In FIG. 31, a thermistor (RS₃ ') 181 is coupled in series with atube current limiting resistor (RS₃) 184. Thermistor 181 may be coupledin parallel with resistor 184 or resistor 184 may be omitted altogether.

As is apparent from discharge starting voltage temperaturecharacteristic curve 143 in FIG. 27, the discharge starting voltage hasa minimum value when the ambient temperataure is about 50° C. That is,when the ambient temperature is higher or lower than about 50° C., thedischarge starting voltage increases. In general, the ambienttemperature (atmospheric temperature or room temperature) can beexpected to range from about 0° C. to about 40° C. If the ambienttemperature falls below about 0° C., it is necessary to increase thedischarge starting voltage. If, in this connection, thermistor 181 inthe circuit in FIG. 31, which may be disposed near the light source 8 inFIG. 1 as shown by a reference numeral 101, has a characteristic thatits resistance is low at low temperature but is high at a hightemperature of about 50° C., then a sufficiently high discharge startingvoltage can be obtained even at low temperature. A cold-cathodedischarge tube suffers from the problem that starting and maintainingthe discharge is difficult at low temperatures, although this problemcan be overcome by coupling a thermistor to the tube.

When the ambient temperature is low, for instance at 0° C. and thedischarge of the cold-cathode discharge tube is started, a high voltageis applied in view of the presence of thermistor 101. Conversely, a lowvoltage is applied to the tube when the ambient temperature is high, forinstance at 50° C. Accordingly, the tube current is high at low ambienttemperatures and less at high ambient temperatures. As is apparent fromthe illumination temperature characteristic curves with the parameter oftube current shown in FIG. 28, the illumination intensity is high whenthe tube current is low. Accordingly, upon starting the discharge at lowambient temperatures, the illumination intensity produced issubstantially equal to that when the ambient temperaturee is high.Similarly, when the ambient temperature is high, the illuminationintensity is substantially equal to that when the ambient temperature islow.

When starting the discharge when the ambient temperature is low, thetube temperature increases due to the discharge after a certain warm-uptime. It is clear from FIG. 28 that if the tube current is constant, theillumination intensity reaches a peak value when the ambient temperatureis about 50° C. However, with a constant ambient temperature, theillumination intensity will increase with an increasing tube current.Accordingly, the illumination intensity immediately after the start ofdischarge is equal to the illumination intensity provided after thewarm-up time after the start of discharge. On the other hand, because ofthe presence of thermistor 101, a large tube current flows when the tubeambient temperature is low, whereas a small tube current flows when thetube ambient temperature is high. Accordingly, at a high temperature,the minimum illumination intensity at that temperature is provided,while at a low temperature, the maximum illumination at that temperatureis provided. Thus, during the warm-up time which elapses from the startof discharge until the tube ambient temperature has reached a stablevalue, the illumination intensity is relatively constant.

After the warm-up time has elapsed after the start of discharge, boththe tube current and the illumination intensity become constant. Thiscan be explained with reference to FIG. 28 described above. As thetemperature increases, the resistance of the thermistor 101 increases asthe tube current decreases. In contrast, as the temperature decreases,the resistance of the thermistor 101 decreases while the tube currentincreases. Accordingly, the amount of heat generated by the cold-cathodedischarge tube is increased and therefore the ambient temperature isincreased. Thus, the tube current, the illumination intensity and thetube ambient temperature become constant at a predetermined period oftime after the start of discharge. If the cold-cathode discharge tube ismaintained lighted, the discharge tube's illumination intensity ismaintained unchanged without being affected by the ambient temperaturewhich is an excellent effect. The tube current is maintained unchangedirrespective of ambient temperature variations and current overloads areavoided. This results in an extended service life of the cold-cathodedischarge tube.

Referring again to FIG. 1, the acrylic resin or polycarbonate resinforming the photoconductor 9 can soften and deform at temperatures ofabout 100° C. This drawback can be eliminated by the employment ofthermistor 101 wherein the temperature of the cold-cathode dischargetube wall and its ambient temperature are not excessively increased andare maintained within acceptable limits by the action of thermistor 101.By maintaining the temperature of the tube wall and its ambienttemperature at substantially constant values as described above, thetemperature of liquid crystal panel 1 is also maintained substantiallyunchanged. Accordingly, the display rate of liquid crystal panel 1 ismaintained without any effect thereon by changes in the ambienttemperature with the result that not only can the user observe thedisplay with ease, but also the liquid crystal display device can beeasily designed and constructed.

As the temperature of a liquid crystal panel is maintained unchanged asdescribed above, for instance in a multiplex application, a margin of20° to 30° C. instead of 0° to 40° C. may be employed for thetemperature characteristic conditions of liquid crystal panel 1. Aresult of this is that a simple temperature compensation circuit can beemployed or the temperature compensation circuit can be omitted.Furthermore, as unwanted condition such as temperature shock which canaffect liquid crystal panel 1 are avoided, the various materials formingliquid crystal panel 1, such as liquid crystal material 7, the sealingagents, polarizing plates 4 and 5 and an adhesive for bonding thepolarizing plates are maintained satisfactory. That is, deterioration isavoided, and there is little if any peeling with the net result that theservice life of the display panel is increased.

As is apparent from the above description, the invention provides thefollowing significant effects:

1. A cold-cathode discharge tube employed as the backlight source has along service life and can be continuously operated. As a cold-cathodedischarge tube emits white light, the display produced by the panel ispleaseing. Moreover, a cold-cathode discharge tube can easily be usedwith color filters to provide a color display, such as with the use of acolored polarizing plate or in a transmission type "guest/host" display.

2. The photoconductor can be made of plastic material, such as acrylicresin or polycarbonate resin, and can be readily manufactured on a largescale.

3. Including a thermistor provides a temperature regulating effect. Thisprovides a tube current limiting effect, constant illuminationintensity, a photoconductor protecting effect and a liquid crystal panelprotecting effect.

These favorable results are also true for the embodiments other thanthat illustrated in FIG. 1.

In order to improve the display further, the scattering and reflectingplate, such as plate 10 in FIG. 1 should be designed so that the lightemitted by the light source is uniformly distributed over the liquidcrystal without increase of the thickness of the device. FIG. 32 is asectional front view of another embodiment according to the presentinvention and FIG. 33 is a sectional side view thereof. In FIGS. 32 and33, a light scattering and reflecting element 217 is provided which canbe a plate of Al, Fe or stainless steel or it can be a plate prepared byplating, vacuum-evaporating or sputtering Al, Fe or Ag on a base metalplate. Alternatively, plate 217 can be manufactured according to one ofthe following methods.

According to a first one of the methods, a transparent plasticphotoconductor of polycarbonate resin or acrylic resin is formed on theinside of the metal plate adapted to reflect light, while on the outsideof the metal plate, a metal foil or a laminated sheet of aluminum andplastic is provided by bonding, mechanical mounting or mechanicalpressure. In a second method, a metal such as Al, Ni or Ag isvacuum-evaporated or sputtered onto a photoconductor. According to athird method, a metal such as Al, Ni or Ag mixed in an adhesive or paintis coated onto a photoconductor.

In another embodiment, the thickness of an opal light scattering element215 is such that, in a direction parallel to a linear light source 216,the central portion is thicker and the two end portions are thinner.With opal light scattering element 215 shaped as described above, itscentral portion is closer to the central portion 218 of linear lightsource 216 which is higher in intensity and accordingly the centralportion is subjected to high intensity light. On the other hand, the twoend portions of opal light scattering element 215 are closer to the ends219 of linear light source 216 which emit no light or emit light of lowintensity and are more remote from central portion 218 of linear lightsource 216 so that the two end portions of element 215 are illuminatedwith a low intensity light. However, the central portion of opal lightscattering element 215 is thicker as described above, and accordinglythe light, being scattered, is transmitted to the end portions while thelight intensity at the central portion is somewhat decreased. On theother hand, the two end portions of opal light scattering element 215are thinner as described above, and accordingly light can satisfactorilypass through the two end portions. Furthermore, the light scattered atthe central portion is transmitted to the two end portions of element215. Thus, the light intensity, due to the scattering effect, isincreased at the two end portions of element 215. As a result, theillumination intensity in the central portion of opal light scatteringelement 215 is substantially equal to that at the two end portions ofelement 215. In other words, the light scattering intensity is uniformthroughout element 215. Accordingly, the liquid crystal display deviceaccording to this embodiment of the invention provides uniformillumination. Therefore, even if the liquid crystal display device isoperated for a relatively long time or is operated continuously, theuser will observe a constant and uniform intensity. As the distancebetween liquid crystal panel 214 and light source 216 is short, theseadvantages may be obtained merely by modifying the configuration of opallight scattering element 215 as described. Therefore, a liquid crystaldisplay device having a uniform illumination intensity effect can bereadily reduced in thickness and accordingly in overall size.

In FIGS. 32 and 33, a semi-transparent reflecting element 222 can bedisposed between liquid crystal panel 214 and opal light scatteringelement 215, if desired. In the daytime when light source 216 need notbe turned on, semi-transparent reflecting element 222 causes thebacklight to scatter and allows a portion of the light to passtherethrough. Therefore, when there is a great deal of ambient lightaround the display device, light source 216 is turned off without usingthe backlight, and only when it is dark around the display device is thelight source turned on to minimize the power consumption of thebacklight. Semi-transparent reflecting element 222 itself has a lightscattering effect. Therefore, the use of semi-transparent reflectingelement 222 placed over opal light scattering element 215 contributesfurther to obtaining uniform light intensity. If the illumination of thebacklight is excessively high, the intensity of light illuminatingliquid crystal panel 214 can be reduced to a suitable value by insertingsemi-transparent refelecting element 222.

FIGS. 34 and 35 are, respectively, a sectional front view and asectional side view of another embodiment of the invention. A liquidcrystal panel 323, a linear light source 324 and an opal lightscattering element 325 are shown. These components are similar inconstruction to those of the embodiment of the invention described withreference to FIGS. 32 and 33. Further in FIGS. 34 and 35, asemi-transparent reflecting element 326 can be inserted, if desired asin the earlier embodiment. A light scattering and reflecting element 327having light scattering and reflecting side elements 328 is provided atboth ends of linear light source 324. Semi-transparent reflectingelement 326 which can be inserted between liquid crystal panel 323 andopal light scattering element 325 are shown as in the embodimentdescribed with reference to FIGS. 32 and 33. A linear light source 324has a light emitting portion 329 and two end portions 330 which emit nolight or emit light at a low intensity which are hereinafter referred toas a "non-emitting portion", when applicable. This embodiment differsfrom the embodiment of FIGS. 32 and 33 in that light scattering andreflecting side elements 328 extend perpendicularly to linear lightsource 324 at both ends of liquid crystal panel 323. As light scatteringand reflecting side elements 328 are provided on both sides of thedisplay device as described above, light is scattered by the two lightscattering and reflecting side elements although linear light source 324has non-emitting portions at both ends. That is, the same illuminatingeffect as in the case where the linear light source has light emittingportions at both ends is obtained. Accordingly, the light intensityproduced is uniform and opal light scattering element 325 can be easilymanufactured. In addition, the thickness of the central portion of theopal light scattering element 325 can be reduced and the backlightportion of the device can be made thinner. Thus, according to thisembodiment of the invention, a small liquid crystal display device withan illuminating unit can be provided. The loss of light is decreased bythe provision of light scattering and reflecting element side 328 on twosides which contributes to an improvement of the efficiency of thedevice.

In FIGS. 36 and 37, a sectional front view and a sectional side viewshowing still another embodiment of the invention are shown. A liquidcrystal panel 431, a linear light source 433, a light scattering andreflecting element 434, an opal light scattering element 42 and asemi-transparent reflecting element 435 which can be inserted betweenliquid crystal panel 431 and opal light scattering element 432 ifdesired are arranged as in the embodiments of FIGS. 32-35. Thisembodiment, however, differs from the those embodiments in theconfiguration of opal ilght scattering element 432. This will bedescribed with reference to FIGS. 38 and 39 in detail which are a frontview and a side view of opal light scattering element 432 shown in FIGS.36 and 37, respectively.

In this embodiment of the invention, the configuration of opal lightscattering element 432 is such that, as shown in FIGS. 38 and 39, in adirection parallel to the longitudinal direction of linear light source433, the central portion is thicker and the end portions are thinner. Ina direction perpendicular to linear light source 433, the centralportion is thicker and the two end portions are thinner. If the diameterof the light emitting portion of linear light source 433 is smallcompared with the width of the gaps at the two ends of liquid crystalpanel 431, irregular illumination is caused in a direction perpendicularto the longitudinal direction of linear light source 433 in the gap ofliquid crystal panel 431.

This effect is more apparent from FIG. 40. As shown in FIG. 40, theupper and lower portions of the displayed pattern "AM 5:45" have darkregions 536 while a middle portion 537 is brighter. Such irregularillumination may be eliminated by increasing the distance between linearlight source 433 and liquid crystal panel 431, although it is impossibleto eliminate completely the irregular illumination in this manner. Inaddition, if the distance is increased, the size of the liquid crystaldisplay device is increased also. However, this problem may be overcomein accordance with this embodiment. Opal light scattering element 432 isso shaped that, in a direction perpendicular to the longitudinaldirection of linear light source 433, the central portion closer to thelight source is thicker and the end portions farther from the lightsource are thinner. Accordingly, a liquid crystal display device whichis free from this irregular illumination and having an excellentillumination effect is provided by this embodiment of the invention.

It will thus be seen that the objects set forth above, and those madeapparent from the preceding description, are efficiently attained and,since certain changes may be made in the above construction withoutdeparting from the spirit and scope of the invention, it is intendedthat all matter contained in the above description or shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed, and all statements of the scope of the invention which, as amatter of language, might be said to fall therebetween.

What is claimed is:
 1. A liquid crystal display device comprising:aliquid crystal display panel; light source means for illuminating saidliquid crystal display panel; a light passage member of one of atransparent and a translucent material, said light passage member beingdisposed between said liquid crystal panel and said light source means;and a light relecting member substantially surounding said light sourcemeans and said light passage member, said light reflecting member havingan opening facing said liquid crystal display panel to expose a surfaceportion of said light passage member, said light passage member andlight reflecting member being adapted to provide light more uniformlyacross said display panel at varying distances from said light sourcemeans with the length of a light path between said light source and saidexposed surface portion being substantially uniform throughout saidlight passage member by reducing the distance between the reflectingmember and the display panel as the distance from the light source meansincreases; wherein the reflecting member is one of a metal plate, ametal film and a lamination sheet of aluminum and plastic adhered tosurface portions of said light passage member other than said opening.2. The liquid crystal display device of claim 1, wherein said liquidcrystal display panel does not overlap said light source means in planview and the thickness of said light passage member decreases as thedistance from said light source increases.
 3. The liquid crystal displaydevice of claim 2, wherein said light passage member and said lightreflecting member are formed with a curved surface in cooperation withthe opening for adjusting the length of the light path.
 4. The liquidcrystal display device of claim 1, wherein said light source meanscomprises an elongated light source and wherein said light passagemember is formed with a space in the light inlet side, said linear lightsource disposed in said space.
 5. The liquid crystal display device ofclaim 1, wherein said light passage member is selected from the group ofmilky colored polycarbonate resins and milky colored acrylic resins. 6.The liquid crystal display device of claim 1, wherein the thickness ofsaid light scattering member is gradually reduced towards end portionsthereof in a direction orthogonal to said light source.
 7. The liquidcrystal display device of claim 1, wherein said light source comprises acold-cathode discharge tube.
 8. The liquid crystal display device ofclaim 1, wherein said reflecting member comprises a metal plate of amaterial selected from the group consisting of Al, Fe and stainlesssteel.
 9. The liquid crystal display device of claim 1, wherein saidreflecting member comprises a metal plate coated with a materialselected from the group consisting of Al, Ni and Ag.
 10. The liquidcrystal display device of claim 1, wherein said light passage member isa transparent plastic resin.
 11. The liquid crystal display device ofclaim 1, wherein said light source means comprises a cold-cathodedischarge tube and said device further includes a wavelength selectionfilter disposed between a liquid crystal layer of said liquid crystalpanel and said light source.
 12. The liquid crystal display device ofclaim 11, wherein said filter comprises a sharp-cut filter for blockingultraviolet rays.
 13. The liquid crystal display device of claim 1,wherein said liquid crystal display panel includes at least one coloredtransparent plate.
 14. The liquid crystal display device of claim 13,wherein said colored plate comprises a dichromatic filter.
 15. Theliquid crystal display device of claim 1, wherein said light sourcecomprises a cold-cathode discharge tube, and said device furtherincludes temperature detector means disposed near a wall of said tubeand voltage control circuit means, said temperature detector beingcoupled to said voltage control circuit means for controlling thedischarge voltage of said tube in respone to change in ambienttemperature.
 16. The liquid crystal display device of claim 15, whereinsaid light passage member is of a material selected from the groupconsisting of acrylic resins and polycarbonate resins.
 17. The liquidcrystal display device of claim 15, wherein said temperature detectormeans comprises a thermistor connected in series with said dischargetube.
 18. The liquid crystal display device of claim 1, including a baseplate and wherein said light source means comprises a cold-cathodedischarge tube mounted to a first side of the base plate facing saidlight passage member, and further comprising discharge stabilizingresistor means mounted on the opposed side of said base plate.
 19. Aliquid crystal display device comprising:a liquid crystal display panel;light source means for illuminating said liquid crystal display panel; alight passage member disposed between said liquid crystal display paneland said light source means; wherein said light source means includes acold-cathode discharge tube and further includes a wavelength selectionfilter disposed between said liquid crystal display panel and said lightsource means.
 20. The liquid crystal display device of claim 19, whereinsaid filter comprises a sharp-cut filter for blocking ultraviolet rays.21. The liquid crystal display device of claim 19, including a baseplate, said cold-cathode discharge tube mounted to a first side of thebase plate facing said light passage member, and further comprisingdischarge stabilizing resistor means mounted on the opposed side of saidbase plate.
 22. The liquid crystal display device of claim 19, whereinsaid liquid crystal display panel includes at least one coloredtransparent plate.
 23. The liquid crystal display device of claim 22,wherein said colored plate comprises a dichromatic filter.
 24. Theliquid crystal display device of claim 19, wherein said device furtherincludes temperature detector means disposed near a wall of said tubeand voltage control circuit means, said tmeperature detector beingcoupled to said voltage control circuit means for controlling thedischarge voltage control circuit means for controlling the dischargevoltage of said tube in response to change in ambient temperature. 25.The liquid crystal display device of claim 24, wherein said lightpassage member is of a material selected from the group consisting ofacrylic resins and polycarbonate resins.
 26. The liquid crystal displaydevice of claim 24, wherein said temperature detector means comprises athermistor connected in series with said discharge tube.
 27. The liquidcrystal display device of claim 19, wherein said light source meansfurther includes resistor means for stabilizing the discharge operationof said cold-cathode discharge tube.
 28. The liquid crystal displaydevice of claim 19, wherein said light source means further includestemperature compensation means for stabilizing the discharge operationof the cold-cathode discharge tube.